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Active potassium extrusion regulated by intracellular pH in Streptococcus faecalis
1Faculty of Pharmaceutical Sciences, Inohana Campus, Chiba University, Japan.
The Journal of Biological Chemistry
|October 5, 1988
Summary
In Streptococcus faecalis, potassium extrusion is an ATP-dependent process that expels potassium ions in exchange for protons. This system is active only when the bacterium
Area of Science:
- Microbiology
- Cell Physiology
- Biochemistry
Background:
- Potassium extrusion in bacteria is crucial for regulating cytoplasmic pH.
- In many organisms, this process involves secondary active transport of potassium for protons.
- Streptococcus faecalis displays a unique mechanism for potassium extrusion.
Purpose of the Study:
- To investigate the mechanism of potassium extrusion in Streptococcus faecalis.
- To determine the conditions and energy requirements for potassium extrusion.
- To elucidate the relationship between cytoplasmic pH and potassium transport.
Main Methods:
- Utilizing glycolyzing Streptococcus faecalis cells.
- Employing alkaline media with permeant weak bases (e.g., methylamine).
- Measuring potassium and [14C]methylamine flux, and cytoplasmic pH changes.
Main Results:
- Potassium extrusion occurred only at alkaline cytoplasmic pH and required ATP generation.
- Permeant weak bases induced potassium extrusion by alkalinizing the cytoplasm.
- Potassium extrusion ceased when cytoplasmic pH normalized, indicating a pH-dependent process.
- [14C]methylamine accumulation was stoichiometrically equivalent to potassium loss.
Conclusions:
- Potassium extrusion in Streptococcus faecalis is mediated by an ATP-driven transport system.
- This system exchanges potassium ions for protons (H+).
- The transport system is specifically active under alkaline cytoplasmic pH conditions.